Organic electronic and optoelectronic materials have been attracting the attention of growing number of researchers for more than 50 years. The design and synthesis of new π-conjugated organic materials, displaying better properties is one of the most investigated subjects. Properties of the organic materials could directly be affected through the modification of the chemical structures of organic compounds Until the mid-1980s, stability and performance of the devices made of organic materials fell short of those devices based on materials such as silicon or gallium arsenide, which was changed with the appearance of a low voltage and efficient thin film light emitting diode. It provided the possibility of using organic thin films for a new generation of electronic and optoelectronic devices. It has now been proven that organic thin films are useful in various applications and organic light emitting device (OLED) is the most successful one, which is used now m full-color displays.
Generally, two groups of organic materials, small molecules and polymers, are used in electronic and optoelectronic devices and allow low cost fabrication of devices (C W. Tang, Appl Phys Letters. 1987, 51, 913-915; J. H. Burroughes, Nature. 1990, 347, 539; U.S. Pat. Nos. 6,727,008, 7,133,032. WO 2007/134280A1; US2005/01184A1; WO9/13148; US005399502; U.S. Pat. No. 4,356,429).
Designing high performance optical and electronic organic devices requires understanding of their electronic structures and even some small tunings in the structure or composition of an organic material can after its original properties enormously. Modification of the structures of the conjugated organic materials to tune their optoelectronic properties is a challenging topic. On the other hand, conjugated polymers pose some problems like reproducibility, purification, and hence electronic properties. Moreover, extra performance might be required to separate of the materials containing conjugated chains of various lengths in order to decrease polydispersity In some cases, to remove the remnant terminal groups by appropriate chemical treatment could be necessary. These extra performances contribute to the increase of the cost and environmental impact of the material. As an alternative, small and soluble conjugated organic molecules could be used in optical and electronic organic devices. Due to their reproducible syntheses and better purification, organic molecules provide more direct and reliable analyses of structure—property relationships, which are the crucial points for high performance organic molecules used in devices.
Thiophene-based organic materials are among the most promising compounds with tunable functional properties by proper molecular engineering Such tuning can also be performed by using fused thienothiophene (TT), dithienothiophene (DTT) as their core skeleton consist of two and more fused rigid thiophene rings and create better π-conjugation and π-π stacking in their solid states to enhance their hole-electron mobility (Skabara, P. J. In Handbook of Thiophene-based Materials; Perepichka, I. F., Perepichka, D. F., Eds.; John Wiley & Sons: Chichester, U.K., 2009; Chapter 3 and Comel, A.; Sommen. G, Kirsch. G. Mini-Rev Org. Chem. 2004, 1, 367-374).
To achieve a substantial breakthrough, design of stable and efficient organic π-conjugated materials with better optical and electronic properties is particularly important. In spite of many luminescent materials exhibiting strong photoluminescence in dilute solutions, their light emission in concentrated solutions or in the solid state are often weakened or almost quenched due to strong π-π stacking, which is known as AIQ, Aggregation Induced Quenching, (T. Forster and K. Kasper, Z. Phys. Chem., 1954, 1, 275 and A. C. Grimslale, K. L. Chan, R E Martin. P G. Jokisz and A. B Holmes, Chem Rev, 2009, 109, 897). On the other hand, Tang and co-workers introduced a new alternative concept, Aggregation-Induced Emission (AIE), which is exactly opposite to AIQ. Organic material emits strong light particularly in its solid or aggregation states. (J. Luo. Z. Xie, J. W. Y Lam, L. Cheng, H. Chen, C. Qiu, H. S. Kwok, X. Zhan, Y. Liu, D Zhu and B. 2 Tang, Chem. Commun., 2001, 1740 and Z. Zhao, Z. Wang, P. Lu, C. Y. K. Chan, D. Liu, J. W. Y. Lam. H. H. Y. Sung, I. D. Williams, Y. Ma and B. Z Tang. Angew. Chem., Int. Ed., 2009, 48, 7608). Tetraphenylethene (TPE), with its simpler molecular structure, is counted among the most effective molecule producing AIE (Y. Dong, J. W. Y. Lam, A. Qin, J. Liu, Z. Li, B. Z. Tang, J. Sun and H. S. Kwok, Appl. Phys. Lett., 2007, 91, 011111). The AIE nature and hole-transport capability of a material, having tetraphenylethylene and Iriphenylamine, have enabled the fabrication of OLEDs devices with simple structures, low-cost and very good performance (Tang Z. B. Adv. Mater. 2010, 22, 19). Thus, it would be desirable developing materials having emissive and hole-transporting multiple functional abilities for organic light emitting diodes. Due to multiple functional properties of these molecules, simple device structures with no extra hole-transporting materials) in order to reduce the fabrication cost, could be fabricated.